Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
A typical cellular wireless network system (wireless communication system) may include a number of base stations with antennas that radiate to define wireless coverage areas, such as cells and cell sectors. Within the wireless coverage areas, a subscriber (or user) accesses the communication services via a wireless communication device (WCD), which can communicate by exchanging radio frequency signals with the base stations. WCDs may include cell phones, tablet computers, tracking devices, embedded wireless modules, and other wirelessly equipped communication devices. In turn, each base station may be coupled with network infrastructure that provides connectivity with one or more communication networks, such as the public switched telephone network (PSTN) and/or a wide area network (WAN) for sending and receiving packet data (the internet, for instance). These (and possibly other) elements function collectively to form a Radio Access Network (RAN) of the wireless communication system. With this arrangement, a WCD within coverage of the RAN may communicate with various remote network entities.
In general, communications on the RAN are carried out in accordance with an air interface protocol that provides procedures for coordinating communications between the base stations and the WCDs. Examples of existing air interface protocols include, without limitation, Code Division Multiple Access (CDMA) (e.g., 1xRTT and 1xEV-DO), Long Term Evolution (LTE), Wireless Interoperability for Microwave Access (WiMAX), Global System for Mobile Communications (GSM), among other examples. Each protocol may define its own procedures for registration of WCDs, initiation of communications, handoff between coverage areas, and other functions related to air interface communication.
Protocols may also define procedures for managing communications from the base stations to the WCDs, which is referred to as an downlink, and for managing communications from the WCDs to the base stations, which is referred to as an uplink.
Depending on the specific underlying technologies and architecture of a given wireless communication system, the RAN elements may also take different forms. In a CDMA system configured to operate according IS-2000 and IS-856 standards, for example, the antenna system is referred to as a base transceiver system (BTS), and is usually under the control of a base station controller (BSC). In a universal mobile telecommunications system (UMTS) configured to operate according to LTE standards, the base station is usually referred to as an eNodeB, and the entity that typically coordinates functionality between multiple eNodeBs is usually referred to as a mobility management entity (MME). In a CDMA system the WCD may be referred to as an access terminal (AT); in an LTE system the WCD may be referred to as user equipment (UE). Other architectures and operational configurations of a RAN are possible as well.
In accordance with the air interface protocol, each coverage area may operate on one or more carrier frequencies (or “carriers”) and may define a number of air interface channels for conveying information between the base stations and the WCDs. These channels may be defined in various ways, such as through frequency division multiplexing, time division multiplexing, and/or code-division multiplexing for instance.
By way of example, each coverage area may have a pilot channel, reference channel or other resource on which the base station may broadcast a pilot signal, reference signal, or other resource WCDs may detect as an indication of coverage and may measure to evaluate coverage strength. As another example, each coverage area may use an access channel, an uplink control channel, or other resource on which WCDs may transmit control messages such as connection requests and registration requests to the base station. And each coverage area may use a downlink control channel or other resource on which the base station may transmit control messages such as system information messages and page messages to WCDs. Each coverage area may then have one or more traffic channels or other resource for carrying communication traffic such as voice data, packet data, and/or other data between the base station and WCDs.
Furthermore, the available spectrum on the air interface can be divided into time-frequency segments to define the various channels, and also for allocation and scheduling purposes. In an LTE system, such time-frequency segments are commonly referred to as resource blocks and span 0.5 milliseconds in time and 180 kilohertz in bandwidth. For example, the base station can evaluate the demands for network resources amongst its served WCDs and then allocate its available resources to those WCDs to accommodate those demands to the extent sufficient resources are available. The control channels may be used to communicate between the WCDs and the base station to facilitate evaluation of the various network demands and also to notify the WCDs of their assigned network resources once resources are allocated.
While communications are generally scheduled by the base station, initiation of communication from a WCD to a base station generally involves at least one unscheduled transmission from the WCD to the base station. In accordance with the air interface protocol, the base stations may provide for a shared access channel on which unscheduled messages can be sent from WCDs to the base station to notify the base station of the WCD's presence in the base station's coverage area (e.g., for registration purposes). Once such an initial unscheduled transmission is received, the base station can then allocate initial uplink and/or downlink resources to communicate with the WCD as necessary to manage further communications. In particular, the WCD may use the initial uplink resources to send information regarding the quantity of network resources sought by the WCD. Such a communication from the WCD is referred to as a service request. The base station can then allocate sufficient network resources to accommodate the service request and send an indication of the allocation to the WCD.
However, in some cases a base station is too loaded with existing network traffic to allocate the resources sought by a WCD. In that case, after receiving an initial communication from the WCD over the access channel, the base station may respond by rejecting the WCD's attempt to connect. After receiving an indication of the base station's rejection, the WCD may then wait for some period before attempting another connection. In practice, after receiving an initial communication over the access channel, the base station may first allocate some initial control channel resources to receive further information from the WCD regarding the nature of the connection sought by the WCD, such as a service request. The base station can then, on the basis of that information, determine whether the base station's network resources are sufficient to accommodate the WCD and respond accordingly.
The access procedure described above, in which an unscheduled transmission is sent over the access channel, is used when a WCD does not already have any network resources, and therefore no means to send an uplink communication to the base station. In practice, this occurs primarily in two circumstances. First, the WCD may have data to transmit over the network, such as occurs when a call or internet session is originated on the WCD and the WCD begins buffering data to send out. Second, the network may receive data to communicate to the WCD, such as occurs when a remote entity initiates a call or other packet data communication addressed to the WCD. In the first case, the WCD may initiate the access procedure on its own in response to having data to send out. In the second case, the network first notifies the WCD that it should initiate the access procedure by sending the WCD a page message addressed to the WCD. Upon receiving the page message, the WCD initiates the access procedure to establish a connection with the network, at which point the data is delivered to the WCD.
As a result, WCDs without ongoing connections to the network continue to monitor particular downlink control channels that are used by the network to send out page messages. As used herein, WCDs with allocated network resources for ongoing communications are said to be operating in “connected mode.” Connected WCDs are able to exchange data with remote entities over the network. On the other hand, WCDs without allocated network resources for ongoing communications are said to be operating in “idle mode.” Idle WCDs monitor downlink control channels for pages and other system information, but do not generally transmit uplink communications back, which also results in reduced power consumption. To conserve network resources, WCDs may generally be configured to default to operating in idle mode, and transition to connected mode when data is ready to transmit or in response to receipt of a page message. Then, following a period of inactivity, the WCD can transition back to idle mode.